The present invention relates to a process for manufacturing clinker enabling CO2 emissions into the atmosphere to be controlled.
Methods for manufacturing clinker are among those industrial processes that emit most CO2, in the same proportions as in the iron and steel industry. Each of them represents the order of 5% of CO2 emissions of man-made origin. This high quantity of CO2 discharge for the cement industry comes not only from the intensive energy consumption in the process for producing clinker, but especially from the reaction for calcining limestone, which emits a very high quantity of CO2 (0.5 tonne of CO2 produced by the mechanism for each tonne of clinker produced). The introduction of new regulations within the framework of the Kyoto protocol requires the various countries that have ratified this protocol to reduce these CO2 emissions, according to fixed objectives per period. Although the short-term objectives seem relatively easy to achieve with primary measures for reducing CO2, the medium and long-term objectives, that are still to be established, could become much more restrictive, especially for industries such as the cement industry. Technological solutions are therefore being currently sought that will enable these future objectives to be achieved for a reasonable cost, that do not endanger the viability of the current sector.
The current solutions envisaged within the context of cement industry installations for reducing their CO2 emissions are of two types. First of all, primary measures that make it possible, for a reasonable cost, to reduce CO2 emissions of the order of a maximum of 15 to 20%; consisting of:                a reduction in the consumption of carbonaceous fuel (improvement of energy yield, substitution of petroleum coke by natural gas)        the increased use of alternative fuels, considered as neutral with regard to the CO2 production cycle (biomass, various types of waste)        the use of substitutes for clinker in the preparation of cement, such as fly ash from thermal power stations and slag from blast furnaces.        
Unfortunately, these techniques do not have the potential for generating reductions in CO2 beyond 15 to 20% and very often come up against logistic problems that do not enable these solutions to be totally permanent.
Secondary measures are currently being studied so as to introduce technologies that will permit a reduction in CO2 emissions that is much more massive, above 50%. The technologies envisaged are generally of two types:                methods for eliminating CO2 from combustion fumes from the process (called “post-combustion”), by washing with amines or by adsorption or liquefaction processes or by membranes,        oxycombustion methods, making it possible to concentrate the gas flow in CO2, by eliminating nitrogen during the combustion process. In this way, this flow may then be composed virtually exclusively of CO2 (after condensation of the vapor) if combustion air is totally replaced by oxygen, or may then be sufficiently enriched in CO2 (in the case of partial substitution of this combustion air) in order to enable more economic use to be made of technologies for separating CO2.        
These secondary methods are for the most part technically proven, often within other application fields, and on more restricted scales, but still with prohibitive costs.
The object of the present invention is to provide a process for manufacturing clinker making it possible for combustion fumes produced by this process to be recovered so as to eliminate CO2 therefrom at a profitable cost.